1. Field of the Invention
The present invention relates to an image forming apparatus for forming hard copy images using an electrophotographic process, and more particularly, it relates to an image forming apparatus having a self-diagnostic function.
2. Description of the Background Art
In general, an electrophotographic process is widely used for a method of forming a hard copy image in an image forming apparatus such as a copying apparatus, a facsimile, an optical printer using a laser beam or an LED array, or the like.
The electrophotographic process includes a charging process for uniformly charging the surface of a photoreceptor, an exposure process of exposing the surface of the photoreceptor in response to image formation for partially removing charges and forming a latent image, a developing process of sticking toner which is contained in a developer to the latent image for forming a toner image, transfer process of transferring the toner image onto a recording paper, and a fixing process of fixing the toner image transferred onto the recording paper.
In an image forming apparatus using such an electrophotographic process, property values such as the surface potential of the photoreceptor, the amount of exposure, toner density and the like corresponding to the respective ones of the aforementioned processes are previously determined in order to obtain a hard copy image having proper (i.e., standard) density, and operation of each mechanical part is defined in response to the property value.
In general, however, specific property values gradually deviate from the determined values, depending on the frequency of employment, environment of the place of installation and the like. In other words, the image density is varied with adhesion of an impurity to the photoreceptor, deterioration of an exposure lamp, stain of mirrors provided in an optical system, time change of the circuit constant of a control circuit, and the like. Further, sudden variation may be caused in the image density.
Therefore, a serviceman operates the image forming apparatus in routine inspection, for example, to confirm the image density from a currently formed hard copy image. In response to the result of the confirmation, he may clean a charger, replace components or change set values of the respective mechanical parts by manipulating dip switches.
In the conventional image forming apparatus, however, the serviceman cannot confirm the density of a hard copy image corresponding to an operating state (condition) previous to the inspection.
Namely, even if the density recognized in the inspection process is different from the proper density, the serviceman cannot confirm whether the difference is abruptly or gradually caused. Consequently, it is difficult to specify the cause (position of nonconformity) for the density change to take proper action. If a temporary expedient is taken in order to obtain a hard copy image of proper density, nonconformity of the apparatus may be increased.